Innovation in surgical robotics has seen a marked paradigm shift from rigid teleoperative systems towards flexible, cooperative and task-specific implementations. While substantial work has gone into the design and control of such systems, significant challenges arise in developing novel end-effector solutions at the scales required, which ultimately limits the sophistication and widespread applicability of these systems. These challenges arise from a general dependence on conventional meso- or micro-scale manufacturing approaches, which are not optimized to develop fully integrated assemblies at mm-scales in a cost-effective manner. Furthermore, developing robust distal sensing modalities that can be easily integrated into mm-scale packages proves to be a significant challenge from a manufacturing and assembly perspective.
Several groups have recognized this challenge and are developing unique solutions to enable distal force sensing for flexible surgical procedures; and a lot of interest has been generated, both academically and commercially, in recent years in using fiber-based optical force sensing methods (such as fiber Bragg gratings, Fabry-Perot interferometry, and light-intensity modulation) for force feedback in catheters and flexible surgical robots and shape estimation of flexible tooling. In 2014, the ThermoCool SmartTouch ablation catheter (BioSense Webster), which employs light intensity modulation to resolve distal forces in 3 axes, achieved FDA-approval to become the first commercially available ablation catheter to feature fiber-based force feedback in real-time. Such a development is a pivotal step towards widespread acceptance and adoption of force sensing methodologies in minimally invasive procedures. While offering unprecedented resolution (<mN) in a compact package, the entire device is designed around optical transmission fibers that occupy valuable space that can otherwise used for working ports or lumens. In addition, expensive interrogators and signal-conditioning equipment are often necessary to convert the signal into a meaningful quantity that can be post-processed. Furthermore, optical fibers are sensitive to deformation for which compensation must be provided (usually with a biasing fiber) to generate a pure reading of the distal force.